South Korea scrambled fighter jets Saturday to intercept a Chinese military reconnaissance plane that spent four hours inside South Korea’s air defense zone, officials said.

The apparent aggression took place just a day after North Korea’s historic pledge to pursue denuclearization of the Korean peninsula in a summit meeting China itself had hailed as “a historic moment.”

South Korean officials met with China’s ambassador and its defense ministry lodged a formal protest against the incursion.

The Chinese plane remained over open waters in the East China Sea for the duration of its flight, approaching the southeastern city of Pohang but avoiding South Korean territory.

Meanwhile, President Donald Trump issued another hopeful tweet about his administration’s negotiation efforts ahead of his anticipated summit with North Korean leader Kim Jong-un.

“Just had a long and very good talk with President Moon of South Korea,” Trump posted at 9:45 am.

“Things are going very well, time and location of meeting with North Korea is being set. Also spoke to Prime Minister Abe of Japan to inform him of the ongoing negotiations.”

A senior US official said Singapore is being considered as a possible venue for the Trump-Kim summit.

North Korea’s official KCNA news agency told the Hermit Kingdom’s populace Saturday that Kim had met with South Korean President Moon Jae-in, declaring their discussion opened the door “for national reconciliation and unity, peace and prosperity.”

But some experts cast doubt on the idea Trump will be dealing with a “born-again North Korea” in his meeting with Kim.

“This is naivety,” Soo Kim, a former CIA analyst on North Korea, told the Sunday Times of London.

“The North Korean leader we saw [Friday] is no different from the leadership we saw in 2000, 2008 — or even just late last year.”